Thick film dielectric compositions for use on aluminum nitride substrates

ABSTRACT

present invention relates to a Cd-free and Pb-free glass composition comprising, based in mol %, 1–10% MO where M is selected from Ba, Sr, Ca and mixtures thereof, 5–30% MgO, 0.3–5% CuO, 0–2.5% P 2 O 5 , 0–2.5% ZrO 2 , 24–45% ZnO, 2–10% Al 2 O 3 , 35–50% SiO 2  and 0.1–3% A 2 O where A is selected from the group of alkali elements and mixtures thereof wherein the glass composition is useful in thick paste dielectric materials which are compatible with AlN substrates.

FIELD OF THE INVENTION

The invention is directed to thick film dielectric compositions for useon aluminum nitride substrates to fabricate multilayer circuits formicroelectronic applications.

BACKGROUND OF THE INVENTION

Recent hybrid packaging technologies concerning thick film materialshave demanded a higher packing density, better performance and thermalmanagement, and a lower cost. Aluminum nitride (AlN) substrates havebeen a promising candidate due to their excellent properties includinghigh thermal conductivity (130–200 Wm⁻¹K⁻¹) and low thermal expansioncoefficient (4–4.5 ppmK⁻¹) particularly for high power applications.This material is suitable for the direct attachment of low thermalexpansion Si/GaAs-based chip carriers. Multilayer hybrid structuresfabricated on AlN substrates provide an excellent solution for highlyintegrated ceramic packaging with good thermal management. Themultilayer structures are achieved by designing electrical circuitpatterns through multiple dielectric thick films printed andsequentially fired on AlN substrates.

Materials associated with aluminum nitride substrates for use inmicroelectronics have been described in some prior art. For example,U.S. Pat. No. 5,089,172 to Allison et al., discloses a thick filmconductor composition adapted to be bonded to an aluminum nitridesubstrate. The conductor composition comprises a metal selected from Au,Cu, Ag, and Pt. Furthermore, the composition comprises from traceamounts up to about 10 wt. % PbO-containing glass frit binder and aLithium compound.

U.S. Pat. No. 5,165,986 to Gardner et al., teaches a conductivecomposition comprising a Cu or Cu alloy, glass binder, and Cd or anoxide of Cd, which may be used on an AlN substrate. The glass taught inGardner is PbO—B₂O₃—SiO_(2.)

U.S. Pat. No. 5,298,330 to Stadnicar, Jr. et al. teaches a thick filmpaste composition adapted to be bonded onto an aluminum nitridesubstrate. The composition requires an electrical property modifier anda glass composition comprising, based on wt. %, 27–56% SiO₂, 20–47.0%BaO, 4.5–25.0% B₂O₃, 0–18% PbO, 0–15% ZnO, and 3–14% Al₂O₃, at leasttrace amounts up to 3% ZrO₂, 0–8% MgO, and 0–12% CaO, among othercompounds within specified ratios.

U.S. Pat. No. 4,808,673 to Hang et. al., teaches a dielectric inkcomposition including a glass composition, based on wt. %, comprising15–25% ZnO, 10–25% MgO, 3–12% BaO or SrO, 5–20% Al₂O₃, 35–50% SiO₂,0.5–3% P₂O₅ and 1–5% ZrSiO₄.

U.S. Pat. No. 4,830,988 to Hang et al., teaches a dielectric ink, foruse on an alumina substrate, comprising glass frit, ceramic filler andorganic vehicle.

U.S. Pat. No. 5,397,830 to Shaikh et al., teaches a thick film paste foruse in producing a dielectric material comprising a glass compositionand a vehicle. The glass composition requires both PbO and Fe₂O₃additions to a SiO₂—Al₂O₃—ZnO—MgO—BaO based dielectric composition.

The glass compositions utilized in the prior art contain elements, suchas Pb and Cd, which are on the EPA hazardous waste list. Furthermore,some of the prior art compositions are not compatible with AINsubstrates. A need therefore exists for AlN substrate-compatible thickfilm dielectric materials, which incorporate a Pb-free and Cd-free glasscomposition, to overcome the disadvantages of the prior art. Anobjective of this invention, therefore, is to provide new and improveddielectric materials which are compatible with AlN substrates. A furtherobject is to provide a Pb-free and Cd-free glass composition for use indielectric materials which are compatible with AlN substrates.

SUMMARY OF THE INVENTION

The glass composition of the present invention may be formulated into athick film composition comprising a dispersion of finely divided solidscomprising:

-   -   (a) glass composition of the present invention; and    -   (b) organic medium.

This thick film composition may further comprise ceramic filler.

Particular useful ceramic fillers are those selected from the groupconsisting of Al₂O₃, ZrO₂, SiO₂, TiO₂, BaTiO₃, cordierite, mullite andmixtures thereof.

The present invention also provides a method of forming a multilayercircuit comprising the steps:

-   -   (a) providing an aluminum nitride substrate;    -   (b) depositing a composition of the present invention on said        substrate;    -   (c) firing said composition and substrate forming an aluminum        nitride article;    -   (d) providing a metallic conductive composition;    -   (e) depositing said conductive composition on said aluminum        nitride article; and    -   (f) firing said aluminum nitrate article and said conductive        composition.

The present invention also provides a multilayer circuit made accordingto the method described immediately above. Also, an article comprisingthe thick film composition with or without filler being present, byprocessing the thick film composition to volatilize the organicpolymeric binder and sinter the glass composition.

The present invention provides a multilayer circuit comprising aplurality of internal thick film metallic conductive composition layersseparated by layers of the thick film composition with or without fillerbeing present, wherein the thick film composition is processed tovolatilize the organic polymeric binder and sinter the glasscomposition.

The multilayer circuit of the present invention, may contain a metallicconductive composition comprises Ag or containing Au.

The present invention provides a method of forming a green tape bycasting a layer of one of the thick film composition of the presentinvention onto a flexible substrate and heating the cast layer to removethe volatile organic solvent therefrom.

A method of forming a green tape by casting a dispersion of a thin layerof a thick film composition of the present invention onto a flexiblesubstrate, heating the cast layer to remove the volatile organic solventtherefrom and separating the solvent-free layer from the substrate.

The present invention provides a method of forming a multilayerinterconnection comprising the steps of:

-   -   (a) forming a patterned array of vias in a plurality of layers        of green tape made by a process of the present invention;    -   (b) filling said vias in the green tape layer(s) of step (a)        with a thick film conductor composition;    -   (c) printing at least one patterned thick film functional layer        over a surface of each of the via-filled green tape layers of        step (b)′    -   (d) laminating the printed green tape layers of step (c) to form        an assemblage comprising a plurality of interconnected        functional layers separated by unfired green tape; and    -   (e) cofiring the assemblage of step (d).

The present invention provides a green tape and a multilayerinterconnection made according to the methods described above.

DETAILED DESCRIPTION OF INVENTION

I. Glass

The present invention relates to a Cd-free and Pb-free glass compositioncomprising, based in mol %, 1–10% MO where M is selected from Ba, Sr, Caand mixtures thereof, 5–30% MgO, 0.3–5% CuO, 0–2.5% P₂O₅, 0–2.5% ZrO₂,24–45% ZnO, 2–10% Al₂O₃, 35–50% SiO₂ and 0.1–3% A₂O where A is selectedfrom the group of alkali elements and mixtures thereof wherein the glasscomposition is useful in thick paste dielectric materials which arecompatible with AlN substrates.

Furthermore, the present invention relates to Cd-free and Pb-free glasscomposition(s) wherein the glass composition(s) are useful in thickpaste dielectric materials which are compatible with AlN substrates. Thealkali-containing zinc aluminosilicate glasses of this invention arenovel and differ from common aluminosilicate glasses in that dielectricsprepared by the glass of the present invention, with or without afiller, have low TCE values (<5 ppmK⁻¹) and are compatible with AlNsubstrates. The components of the glass are based in mol %, 1–10% MOwhere M is selected from Ba, Sr, Ca and mixtures thereof, 5–30% MgO,0.3–5% CuO, 24–45% ZnO, 0–2.5% P₂O₅, 0–2.5% ZrO₂, 2–10% Al₂O₃, 35–50%SiO₂ and 0.1–3% A₂O where A is selected from the group of alkalielements, for example, Li, Na and K, and mixtures thereof.

The large contents of zinc and silicon in glass are believed to providea low TCE value (<5 ppmK⁻¹). Other cations with +2 charges, such as Ba,Sr, Ca, Mg and Cu, in glass are effective in modifying glass structureand properties. In particular, the existence of alkali oxides improvessensitivity of the glass to heating condition by controlling thedensification and crystallization behavior of the resulting tapes. Thecrucial role of the alkali addition is to provide required flow anddensification characteristics to the resultant thick films at itsdesired firing temperature. It performs the function of glass viscosityadjustment without affecting required physical and electricalperformance of the tape.

The glasses described herein are produced by conventional glass makingtechniques. More particularly, the glasses may be prepared as follows.Glasses were typically prepared in 500–2000 gram quantities. Typically,the ingredients are weighted then mixed in the desired proportions andheated in a bottom-loading furnace to form a melt in platinum alloycrucibles. Heating is typically conducted to a peak temperature(1400–1600° C.) and for a time such that the melt becomes entirelyliquid and homogeneous. The glass melts are quenched by counter rotatingstainless steel roller to form a 10–20 mil thick platelet of glass. Theresulting glass platelet is then milled to form a powder with its 50%volume distribution set between 1–5 microns. The glass powders are thenformulated with optional filler and organic medium into a thick filmcomposition (or “paste”). The glass composition is present in the amountof about 43 to about 85 wt. %, based on total composition.

The glass described herein is also compatible with silver or gold-basedconductors. The glass in the thick film does not flow excessively uponfiring. There is no conductor staining problem with the glass afterfiring.

II. Dielectric Thick Film Composition and Application

The invention is further directed to the glass composition (as describedabove) incorporated in a thick film composition (sometimes referred toas “pastes”) comprising a dispersion of finely divided solidscomprising, based on solids: (a) 80–100 wt. % the glass composition; (b)0–20 wt. % ceramic filler; both dispersed in a solution of (c) anorganic polymeric binder; and (d) a volatile organic solvent.Furthermore, the thick film composition of the present inventionprovides glass and ceramic materials that are free of elements, such asPb and Cd, which are on the EPA hazardous waste list. The components ofthe dielectric thick film composition are discussed herein above andbelow.

The main components of the thick film dielectric composition are (a) aglass powder dispersed in (b) an organic medium. A ceramic filler may beoptionally added to modify the properties of the thick film composition.In most cases, glass is the main part of the dielectric, whichdetermines its performance and compatibility with substrates andconductors. Primarily glass provides a low densification temperaturebelow 900° C. and appropriate thermal and electrical properties. Theglass of the present invention is described in Section I above. Ceramicfiller may be used to modify the behavior of the glass for bettercompatibility with contacting substrates. There are two importantparameters, which must be considered for the design of dielectriccomposition, thermal expansion match and chemical reactivity with AlN.The TCE mismatch between dielectric and AlN can induce cracking andother major failures in the circuitry. The reactivity of glass with AlNmakes the glass choice more difficult because the substrate near thedielectric has a strong tendency to oxidation with oxide-based glassesin the dielectric. Some reaction with the surface of AlN is required toprovide bonding of the dielectric layer, but excessive reaction with thenitride surface is known to produce adverse conditions such asblistering and loss of bonding. Additional constraints on the dielectricapply when a multilayer dielectric may be employed. Additional needs forcompatibility with conductors and passive buried components adds to thecomplexity of the requirements.

Generally, a thick film composition comprises a functional phase thatimparts appropriate electrically functional properties to thecomposition, which is dispersed in an organic medium. The functionalphase comprises the functional solids dispersed in an organic medium,which act in the composition as a carrier for the functional phase.Furthermore, the thick film composition of the present invention mayalso comprise ceramic filler.

The thick film composition of the present invention is ascreen-printable dielectric composition, which forms a multilayerstructure on AlN substrates. The dielectric thick film composition, asdescribed herein, may be bonded to an AlN substrate by depositing thethick film composition onto the substrate and firing the substrate.Furthermore, a multilayer circuit may be formed which utilizes the thickfilm composition of the present invention by providing a metallicconductor composition, including base metal conductors such as Ag or Au,to produce a functional electronic circuit on an AlN substrate. Amultilayer circuit may be formed by the following method comprising thesteps: (a) providing an Aluminum nitride substrate; (b) depositing thethick film composition as described herein on said substrate; (c) firingthe composition and substrate forming an aluminum nitride article; (d)providing a metallic conductive composition; (e) depositing theconductive composition on the aluminum nitride article; and (f) firingthe aluminum nitrate article and the conductive composition. Themultilayer circuit may comprise a plurality of layers of interconnectedelectronic circuitry, each separated by the dielectric thick filmcomposition of the present invention.

Ceramic Filler

Ceramic filler may also be added to the thick film composition of thepresent invention. Ceramic oxide filler such as Al₂O₃, ZrO₂, SiO₂, TiO₂,BaTiO₂, cordierite, mullite and mixtures thereof are typically added tothe dielectric composition in an amount of 0–20 wt. % based on solids.The filler controls physical, thermal and electrical properties of thethick film over the given measurement condition. The glass and ceramiccomponents of the composition form a glass-ceramic structure duringfiring by forming crystalline phases, which lead to a low TCE and asufficient mechanical integrity.

Al₂O₃ is the chosen ceramic filler, since it may partially react withthe glass to form an Al-containing crystalline phase or modify thesintering behavior. Al₂O₃ is very effective in providing high mechanicalstrength and inertness against detrimental chemical reactions. Anotherfunction of the ceramic filler is rheological control of the systemduring firing. The ceramic particles limit flow of the glass by actingas a physical barrier. They also inhibit sintering of the glass and thusfacilitate better burnout of the organics. Other fillers, α quartz,CaZrO₃, mullite, cordierite, forsterite, zircon, zirconia, yttria orcalcia-stabilized zirconia, CaTiO₃, MgTiO₃, SiO₂, and amorphous silicamay be used by themselves or in mixtures to modify thick filmperformance and characteristics.

In the formulation of thick film compositions, the amount of glassrelative to the amount of ceramic material is quite important. Theceramic filler range of 0–20% by wt. based on solids is consideredpreferable in that sufficient densification and good electricalperformance are achieved. Typically, if the filler concentration exceeds20% by wt., the fired structure is not sufficiently densified and tooporous. In the case of alumina filler, the filler level of 1–5% by wt.based on solids is desirable in that full densification can be achievedat the firing temperature of 850° C. without creating blisters on thetop surface of fired samples. The thick film composition may comprise upto 17 wt % ceramic filler based on total composition.

For the purpose of obtaining higher densification of the compositionupon firing, it is important that the inorganic solids have smallparticle sizes. In particular, substantially none of the particlesshould exceed 15 μm and preferably not exceed 10 μm. Subject to thesemaximum size limitations, it is preferred that at least 50% of theparticles, both glass and ceramic, be greater than 1 μm and preferablyin the 2–5 μm range.

In addition to the filler, a coloring agent such as Cu₂O, Co-aluminateand CoO may be added for cosmetic effects when needed.

Organic Medium

The organic medium in which the glass and ceramic inorganic solids aredispersed is comprised of the polymeric binder which is dissolved in avolatile organic solvent and, optionally, other dissolved materials suchas plasticizers, release agents, dispersing agents, stripping agents,antifoaming agents and wetting agents.

The solids are typically mixed with an organic medium by mechanicalmixing to form a pastelike composition, called “pastes”, having suitableconsistency and rheology for printing. A wide variety of inert liquidscan be used as organic medium. The organic medium must be one in whichthe solids are dispersible with an adequate degree of stability. Therheological properties of the medium must be such that they lend goodapplication properties to the composition. Such properties include:dispersion of solids with an adequate degree of stability, goodapplication of composition, appropriate viscosity, thixotropic,appropriate wettability of the substrate and the solids, a good dryingrate, good firing properties, and a dried film strength sufficient towithstand rough handling. The organic medium is conventional in the artand is typically a solution of the polymer in solvent(s). The mostfrequently used resin for this purpose is ethyl cellulose. Otherexamples of resins include ethylhydroxyethyl cellulose, wood rosin,mixtures of ethyl cellulose and phenolic resins, polymethacrylates oflower alcohols, and monobutyl ether of ethylene glycol monoacetate canalso be used. The most widely used solvents found in thick filmcompositions are ethyl acetate and terpenes such as alpha- orbeta-terpineol or mixtures thereof with other solvents such as kerosene,dibutylphthalate, butyl carbitol, butyl carbitol acetate, hexyleneglycol and high boiling alcohols and alcohol esters. In addition,volatile liquids for promoting rapid hardening after application on thesubstrate can be included in the vehicle. The preferred mediums arebased on ethyl cellulose and β-terpineol. Various combinations of theseand other solvents are formulated to obtain the viscosity and volatilityrequirements desired.

The ratio of organic medium in the thick film composition to theinorganic solids in the dispersion is dependent on the method ofapplying the paste and the kind of organic medium used, and it can vary.Usually, the dispersion will contain 60–85 wt % of inorganic solids and15–40 wt % of organic medium in order to obtain good coating. Withinthese limits, it is desirable to use the least possible amount of bindervis-à-vis solids in order to reduce the amount of organics which must beremoved by pyrolysis and to obtain better particle packing which givesreduced shrinkage upon firing.

The thick film composition is fired to burn out the organics and toimpart the electrically functional properties. The glass baseddielectric thick film paste is also suitable for firing in inert oroxidizing atmosphere. The resultant multilayer thick film dielectrics,after firing, demonstrate good densification and compatibility withsilver and gold metallizations.

Prior to firing, a processing requirement may include an optional heattreatment such as drying, curing, reflow, soldering and others known tothose skilled in the art of thick film technology. “Organics” comprisepolymer or resin components of a thick film composition.

III. Green Tape Composition and Applications

The thick film composition can be used to fabricate ceramic tapesubstrates for applications utilizing LTCC (low temperature co-firedceramics) technology. When used in this application it may be termed“green tape.” The LTCC tape consists of glass and ceramic filler (andorganic medium prior to firing). The glass from above is one componentof the composition. A proper choice of ceramic filler is required toproduce good dimensional stability and high mechanical strength. Ceramicfiller such as those listed above may also be used in green tapeapplications. A desirable range of glass/filler ratios is determineddepending on the properties desired in the fired specimens. A fillerrange of 20–60% by weight solids is considered desirable in thatsufficient densification is achieved. If the filler concentrationexceeds 60% by wt., the fired structure is not sufficiently densifiedand is too porous.

A green tape is formed by casting a thin layer of a slurry dispersion ofthe glass, polymeric binder and solvent as described above onto aflexible substrate, heating the cast layer to remove the volatilesolvent and then separating the solvent-free layer from the substrate.The green tape is used primarily as a dielectric or insulating materialfor multilayer electronic circuits. A roll of green tape is blanked withregistration holes in each corner to a size somewhat larger than theactual dimensions of the circuit. To connect various layers of themultilayer circuit, via holes are formed in the green tape. This istypically done by mechanical punching. However, a sharply focused lasercan be used to volatilize the green tape. Typical via hole sizes rangefrom 0.006″ to 0.25″. The interconnections between layers are formed byfilling the via holes with a thick film conductive ink (composition).This ink is usually applied by standard screen printing techniques. Eachlayer of circuitry is completed by screen printing conductor tracks.Also, resistor inks or high dielectric capacitor inks can be printed oneach layer to form resistive or capacitive circuit elements. Also,especially formulated high dielectric constant green tapes similar tothose used in the multilayer capacitor industry can be incorporated aspart of the multilayer circuitry.

After each layer of the circuit is completed, the individual layers arestacked and laminated. A confined pressing die is used to insure precisealignment between layers. The laminates are trimmed with a hot stagecutter. Firing is carried out in a standard thick film conveyor beltfurnace or in a box furnace with a programmed heating cycle forming afired article.

As used herein, the term “firing” means heating the article in anoxidizing atmosphere such as air to a temperature and for a timesufficient to volatilize (burn-out) the organic material in the layersof the assemblage to sinter any glass, metal or dielectric material inthe layers and thus densify the dielectric layer.

It will be recognized by those skilled in the art that in each of thelaminating steps the layers must be accurate in registration so that thevias are properly connected to the appropriate contact points of theadjacent functional layer.

The term “functional layer” refers to the layers printed on the ceramicgreen tape which have either conductive, resistive or capacitivefunctionality. Thus, as indicated above, a typical green tape layer mayhave printed thereon one or more resistor circuits and/or capacitors aswell as a conductive circuit.

The present invention will be discussed in further detail by givingpractical examples. The scope of the present invention, however, is notlimited in any way by these practical examples.

EXAMPLES Examples 1–12

A series of alkali-containing zinc aluminosilicate glass compositionsthat have been found to be suitable in the present invention forapplication to thick film paste are shown in Table 1. All glasses wereprepared by mixing raw materials and then firing in a platinum crucibleat 1450–1550° C. The resulting melt was stirred and quenched by pouringon the surface of counter rotating stainless steel rollers or into awater tank. The glass powders prepared for the invention were adjustedto a 1–3 μm mean size by wet milling using alumina ball media prior toformulation as a paste. The wet slurry after milling was dried in a hotair oven and deagglomerated by the sieving process.

The glass density has been measured by the Archemedes method utilizingthe volume displacement when a glass sample is weighed while suspendedin water and dried to compute its density in grams per cubic centimeter.

The glass was further characterized by DTA (Differential ThermalAnalysis) to investigate crystallization behavior during firing. DTA hasbeen used frequently in demonstrating crystallization behavior ofcertain glasses with regard to crystallization temperature andcrystallization kinetics. As a result, two distinct exothermic peaks atabout 820° C. and 970° C. were found in the DTA output plots of thetested glass examples 6–10, suggesting the occurrence of crystallizationfrom the glassy state. The crystalline phase is believed to be based onzinc magnesium silicates. The crystallization behavior is an importantcharacteristic of the glass composition for this application and can beattributed to physical property benefits, such as high mechanicalstrength and good dimensional control of the dielectrics, which areknown to be particularly important in multilayer dielectrics.

TABLE 1 Glass composition in mol % Ex. # 1 2 3 4 5 6 7 8 9 10 11 12 SiO₂41.1 40.2 40.4 41.3 37.2 42.4 42.3 44.8 42.4 42.4 42.4 42.4 Al₂O₃ 5.75.8 5.9 5.7 2.8 5.7 5.6 4 5.7 5.7 5.7 5.7 ZnO 30.8 30.6 30.6 30.7 43.230.4 30.4 30 24.1 30.5 30.5 30.5 MgO 17.9 18 17.8 17.8 8.8 17.7 17.617.4 24.1 17.7 17.7 17.7 CuO 0.9 0.9 0.9 0.9 3.9 0.9 1.4 0.8 0.8 0.8 0.80.8 BaO 2.5 2.5 2.4 2.5 1.2 2.4 2.4 2.4 2.4 2.4 SrO 2.4 CaO 2.4 Na₂O 0.60.6 0.6 0.6 2.9 0.5 0.3 0.6 0.5 0.5 0.5 K₂O 0.5 P₂O₅ 0.7 1.2 0.5 0.2ZrO₂ 1.1 0.4 Density (g/cc) — — — — 3.68 3.36 3.41 3.38 3.45 3.37 3.333.36

Examples 13–23

Dielectric thick film paste was prepared by mixing glass and ceramicfiller with organic media based on the mixture of Texanol® solvent andethyl cellulose resin. In addition, coloring agent such as co-aluminateand cobalt oxide was used to have cosmetic effects. Table 2 representsthe examples of thick film compositions. The dielectric paste wasprinted on an AlN substrate, dried at 120° C. for solvent evaporation,and then fired at a peak temperature of 850° C. for 10 minute in aconventional profile of 30 or 60 minutes. The ceramic fired dense andshowed good adhesion with AlN substrate. No cracking or blistering wasobserved on the surface of fired thick films.

The fired thick films were further characterized using various patternsof commercially-available DuPont conductors such as ALN11 (Ag), ALN21(Ag—Pt), ALN33(Ag—Pd), and 5771 (Au). The conductors were screen-printedon the top or bottom of the dielectric and fired separately at the sameheating profile (30 minutes) and peak temperature (850° C.). Allconductors showed good compatibility with the dielectric thick film. Nosilver stains or cracks were particularly observed around the pattern ofAg-based conductors.

Table 3 shows the electrical performance of selected samples of Examples13–23. Low frequency dielectric characteristics were evaluated using animpedance analyzer (Hewlett Packard 4284A) within the frequency range of1 kHz to 13 MHz. For the dielectric property testing, a capacitor thickfilm structure sandwiched by a Ag-based conductor was fabricated andmeasured at room temperature with a change in frequency. Resultingdielectric constant ranged from 5 to 7 at 1 MHz. No significantvariations in the dielectric constant and loss tangent were observedover the frequency range and thick film composition. Values in breakdownvoltage and electrical resistance showed excellence regardless of samplecomposition. Breakdown voltage was measured using an AC/DC HIPOT tester(Model HD115/A) by increasing applied voltage for the same samples usedfor dielectric property measurement. A HP3457A multimeter was used forthe measurement of electrical resistance.

Specifically, the Examples 15–17 demonstrate the effect of differentcontents of alumina filler on thick film performance. Increasing thecontent of ceramic filler tends to generate channels for easy burn-outof the organics during firing and result in blister-free thick films.But excessive amounts of alumina filler showed an increase in dielectricloss due presumably to the decreased hermeticity of thick films.

TABLE 2 Solids composition in weight % Ex. # 13 14 15 16 17 18 19 20 2122 23 Glass Ex. # 1 2 6 6 6 6 6 7 8 9 10 Glass 71.0% 71.0% 71.0% 68.0%65.0% 71.0% 71.0% 71.0% 71.0% 71.0% 71.0% Al₂O₃  1.5%  1.5%  1.5%  4.5% 7.5% — —  1.5%  1.5%  1.5%  1.5% ZrO₂ — — — — —  1.5% — — — — —Cordierite — — — — — —  1.5% — — — — Co-aluminate  1.5%  1.5%  1.5% 1.5%  1.5%  1.5%  1.5%  1.5%  1.5%  1.5%  1.5% Surfactant  0.7%  0.7% 0.7%  0.7%  0.7%  0.7%  0.7%  0.7%  0.7%  0.7%  0.7% Binder Resin  1.3% 1.3%  1.3%  1.3%  1.3%  1.3%  1.3%  1.3%  1.3%  1.3%  1.3% Solvent24.0% 24.0% 24.0% 24.0% 24.0% 24.0% 24.0% 24.0% 24.0% 24.0% 24.0%

TABLE 3 Characteristics of thick films Ex. # 13 14 15 16 17 18 19 20 2122 23 Dielectric 5.7 5.9 5.8 5.9 6.2 6.1 — 6.1 5.9 — 5.9 Constant (at 1MHz) Loss tangent <0.3% <0.3% <0.3% <0.3% <0.5% <0.3% <0.3% <0.3% <0.3%<0.3% <0.3% (at 1 MHz) Insulation    >10¹²    >10¹²    >10¹²    >10¹²   >10¹²    >10¹²    >10¹²    >10¹²    >10¹²    >10¹²    >10¹²resistance Ω (at 100 V DC)Breakdown >1000 >1000 >1000 >1000 >1000 >1000 >1000 >1000 >1000 >1000 >1000Voltage, V/25 μm

1. A glass composition comprising, in mol %, 1–10% MO where M isselected from Ba, Sr, Ca and mixtures thereof, 5–30% MgO, 0.3–5% CuO,0–2.5% P₂O₅, 0–2.5% ZrO₂, 24–45% ZnO, 2–10% Al₂O₃, 35–50% SiO₂ and0.1–3% A₂O where A is one or more alkali metal elements.
 2. A thick filmcomposition comprising a dispersion of finely divided solids comprising:(a) glass composition as in claim 1; and (b) organic medium.
 3. Thethick film composition of claim 2 further comprising ceramic filler. 4.The thick film composition of claim 3 wherein said ceramic fillercomprises up to 17 wt. % of the total composition.
 5. The thick filmcomposition as in any one of claim 2, 3, or 4, wherein said glasscomposition comprises 43–85 wt. % of the total composition.
 6. The thickfilm composition as in any one of claim 2, 3, or 4, wherein said organicmedium comprises 15–40 wt. % of the total composition.
 7. The thick filmcomposition of claim 2 wherein the ceramic filler is selected fromAl₂O₃, ZrO₂, SiO₂, TiO₂, BaTiO₃, cordierite, mullite, and mixturesthereof.